1. Field of the Invention
The present invention relates to a one side surface molten metallic coating apparatus for coating on one side only of a substrate such as a sheet or strip of metal.
2. Description of the Prior Art
It has been developed to use strips coated on one side only which are prepared by coating a molten metal on one side only to improve anticorrosive and soldering characteristics and which are used in cars and household electric instruments etc.
An electric plating process has been known as the process for preparing a strip of metal coated on one side only. In the electric plating process, the productivity is low and the cost is high in order to prepare a sheet or strip of metal on which a large amount of molten metal is coated. Moreover, the process could not applied for coating aluminum etc.
On the contrary, if a hot dipping process for coating a strip of metal by immersing it in a molten metal bath, can be applied on one side only, the advantages are remarkable from the economical and technical viewpoints. Various processes have been proposed.
U.S. Pat. Nos. 3,149,987 and 3,121,019 disclose the processes for coating on one side only by coating sodium bentonite or an alkaline earth hydroxide on a rear surface to form a coating and immersing it in a molten metal bath and then, removing the coating of sodium bentonite or an alkaline earth hydroxide. These processes include the step of coating a resist on the rear surface and the step of removing the resist after the molten metallic coating whereby the processes are remarkably complicated and the resist coated on the rear surface contaminates the molten metal bath and the contaminated molten metal is coated to cause difficulties.
It has not been found any satisfactory process for coating a molten metal on one side only.
In order to overcome the disadvantages, it has been developed to apply a process for coating on one side only by contacting one side only of a substrate with a molten metal bath which is locally raised by applying ultrasonic vibration to the molten metal.
However, when the coating process is continuously applied for a long time, the edge of the tool for ultrasonic vibration is gradually wore and an uniformly coated product can not be obtained.